Metal Crucible Research Articles

Bulk Single-Crystal Growth of Ce/Gd3(Al,Ga)5O12 from Melt without a Precious Metal Crucible by Pulling from a Cold Container

We report the growth of cerium-doped multicomponent garnet (Ce/GAGG) single crystals based on crystal pulling from a melt using a cold container without employing a precious metal crucible. This novel method is described in detail. We measured the optical, luminescence, and scintillation characteristics of several samples cut from three crystals and compared them with a commercial Ce/GAGG crystal. The best samples from the set are fully comparable in all characteristics with the commercial reference crystal, demonstrating the practical potential of this method. Avoidance of an expensive precious metal crucible in this method makes crystal growth much more economical.

Microstructural Effects of Controlled Dilution of High Strength Steel Wire into S960QL

Controlled dilution experiments were conducted in a novel manner that allowed for precise dilution of base material into the wire consumables, enabling for a prompt analysis of microstructural trends as dilution is altered. Different heat cycles and cooling rates of the wire material, without base metal additions, were shown to cause different microstructures, varying from parallel plates to random or interlocking orientation, with varying size of packets. The proposed method enables more controlled conditions with a known dilution value from mass percentages. Chopped filler wire is weighed and added to the base metal crucible, base metal chips are also weighed and added to the filler wire in specific mass percentages. A pulsed laser irradiates the metal, melting the mixture into a sample nugget. Lack of fusion is a benefit in this method as contamination from the base plate is negligible. The cooling rate is influenced by the pulse shape, and can be used to reheat the nugget, demonstrating the microstructural evolution in a complex thermal cycle. This method is demonstrated for S960QL steel with under-matched wire consumable, generally used for laser-arc hybrid processes to obtain high toughness, where a representative thermal cycle is needed. The thermal cycle is measured via a remote process, Dualscope, to evaluate the spacial temperature of the surface. The microstructures found using the snapshot method are similar to those found in the narrow gap multi-layer weld, different only in the size of the grains and packets.

Numerical Simulation of Slurry Making Process of 7075 Aluminum Alloy under Electromagnetic Field in Rheocasting Process

Rheocasting processes have several technological advantages, such as shorter processing and lower cost than thixocasting processed, while better product quality than conventional die casting. At present, the common alloys used in rheocasting processes are mainly Al-Si alloys which have limited strength. There is a strong demand for higher strength aluminum alloys in industries, for instance the 7075 aluminum alloy. However, the solid fraction of the 7075 aluminum alloy varies significantly with the temperature change in the medium solid fraction range from 0.4 to 0.6, which poses a great challenge to the slurry preparation. The enthalpy compensation process, in which the core was electromagnetic heating in the outside of the metallic crucible containing aluminum alloy melt, has been proposed to reduce the temperature difference within semi-solid slurry in this work. This study used simulation method to analyze the effects of key process parameters on the temperature difference within the 7075 aluminum alloy slurry. The simulation results indicated that semi-solid slurry with medium solid fraction may be obtained and temperature difference may be reduced to less than 4°C.

Thermal Analysis for the Prediction of Grain Refinement: An Experimental Investigation on an AlSiMg Foundry Alloy

Thermal analysis is widely used as a prediction tool for the quality of Al alloys before casting. In the present work, the effects of different grain refiners on the characteristic temperatures and on the grain size of α-Al phase were studied by thermal analysis and metallographic investigations. The response of an AlSiMg alloy towards grain refiners, added in form of rods and tabs, was investigated. In foundry practice, the fading phenomenon of grain refiners is well-known but not completely understood. For these reasons, the fading effect of each refiner at 60 minutes and 120 minutes holding times was also studied. Cooling curves and their derivatives were obtained during solidification of the alloys in a metallic crucible. Experimental data indicated the increase of the temperature associated with the nucleation of α-Al dendrites for the grain-refined alloys in comparison to the untreated ones. Simultaneously, a decrease in primary Al growth temperature, that led to the disappearance of the minimum temperature, were observed. Microstructural features revealed that an increase of 6 ÷ 7 °C of the nucleation temperature, compared to the not refined alloy, corresponds to a significant decrease in average grain size.

Stimulation of densification during the reduction of U3O8 to UO2 by atmosphere control

A reduction process in the head-end for pyroprocessing has been adopted to avoid oxidation attack on the molybdenum crucible during sintering. The reduction process is employed to reduce U3O8 pellets to UO2 prior to sintering. This allows elimination of the oxygen source, which causes oxidation attack during sintering, thereby permitting the use of a metallic crucible. However, little densification occurs due to the low reduction temperature limited by the INCONEL crucible. Consequently, the amount of material scraps from the pellets increases, thus creating an additional processing burden due to its high radioactivity. To reduce the amount of scraps, densification should be enhanced. This study suggests a simple atmospheric control strategy and clarifies its effects. With the atmospheric control, a higher bulk density and better attrition resistance were obtained in comparison to without this strategy. This can be explained in terms of O/U ratio dependent diffusion kinetics during the reduction of U3O8 to UO2.

Statistical analysis of the effects of graphite crucible on viscosity measurement of silicate melts

Graphite crucible is widely used in high temperature viscosity measurement due to its low cost. However, it may cause measurement errors because of contamination with fine graphite particles, non-wetting conditions, or chemical reactions between melt and graphite. In order to clarify the effect of graphite crucible on viscosity measurement, in this work, more than 800 compositions and 3300 viscosity measurements within CaO-MgO-Al2O3-SiO2 systems were collected and analyzed, using a statistical and modeling-based way. It is found the viscosity data obtained in graphite crucible show much larger scatter than those obtained in metal crucibles. Averagely, viscosity obtained in graphite crucible is 24% higher. The chemical reaction SiO2(l) + 3C(s) = SiC(s) + 2CO(g) is the primary error source for viscosity measurement in graphite crucible. It is suggested that the viscosity data obtained in graphite crucible can be used only with great caution.

Effects of Grain Refiner on the Microstructural Evolution during Making Semi-Solid Slurry of the A357 Alloy

The enthalpy equilibration method is a novel technique to produce globular grain structure in semi-solid slurry preparation. In this process, the liquid is firstly poured into a metallic crucible, which possesses low thermal conductivity and high thermal capacity. Homogeneous distribution of temperature within the metallic crucible is achieved by rotating the crucible and cold down to a temperature between liquidus and solidus, determined by the requirement of solid fraction. The semi-solid slurry is then transferred to a high pressure die caster. In order to achieve a spherical microstructure morphologies in the entire slurry, effects of grain refiners, in addition to the enthalpy equilibration method, on the microstructure of the slurries of A357 alloy were investigated. Quantitative metallographic measurements were applied to evaluate microstructural evolution and processing parameters were optimized.

Scaling-Up of Bulk β-Ga2O3 Single Crystals by the Czochralski Method

We present a new approach for scaling-up the growth of β-Ga2O3 single crystals grown from the melt by the Czochralski method, which has also a direct application to other melt-growth techniques involving a noble metal crucible. Experimental and theoretical results point to melt thermodynamics as the crucial factor in increasing the volume of a growing crystal. In particular, the formation of metallic gallium in the liquid phase in large melt volumes causes problems with crystal growth and eutectic or intermetallic phase formation with the noble metal crucible. The larger crystals to be grown the higher oxygen concentration is required. The minimum oxygen concentration ranges from about 8 to 100 vol.% for 2 to 4 inch diameter cylindrical crystals, challenging the use of iridium crucibles in a combination with such high oxygen concentrations. A specific way of oxygen delivery to a growth furnace with the iridium crucible allows to minimize the formation of metallic gallium in the melt and thus obtaining large crystal volumes while decreasing the probability of the eutectic formation.

Influence of crucible and coil geometry on the induction heating process in Czochralski crystal growth system

A 2D finite element method is employed to compute electromagnetic field as well as volumetric heat generation in an oxide Czochralski crystal growth system considering different shapes of metal crucible and different configurations of induction coil. The results show undeniable roles of crucible corner shape and setup of the RF-coil under the crucible in producing desirable heat pattern and avoiding common issues in the CZ growth systems.

The robustness of the two‐colour assumption in pyrometry of solidifying AISI D2 alloy droplets

A drop tube‐impulse atomization technique was used to produce D2 tool steel powders. Shadowgraph (Sizing Master Shadow from LaVision GmbH in Göttingen, Germany) was utilized to measure in‐situ velocity and droplet size. Simultaneously, the DPV‐2000 (Tecnar Automation Ltée, St. Hubert Quebec, Canada) was used to measure the radiant energy and droplet size of atomized droplets. These devices were mounted on a 3D translation stage which was designed, constructed and installed in the drop tube. The measurements were done at three different distances from the molten metal crucible, 4 cm, 18 cm and 28 cm. A thermal model of droplet cooling was coupled with the temperature of primary phase undercooling for D2 tool steel. The results from this model were used in order to find the emissivity behaviour of the droplets. It is shown that emissivity of the droplets is a function of size and temperature. It was concluded that the DPV‐2000 should be considered as a single color pyrometer since the gray body assumption for D2 tool steel falling droplets using DPV‐2000 during is invalid for the range of measurements taken.

A novel crystal growth technique from the melt: Levitation-Assisted Self-Seeding Crystal Growth Method

A novel melt crystal growth technique was developed and applied for growing bulk In2O3 single crystals. In this new method the In2O3 starting material inside an inductively heated metal crucible is subjected to a controlled decomposition in such a way that a certain amount of free metallic indium forms. As a result, the electromagnetic field from an RF coil couples also to the In2O3 starting material, in addition to the metal crucible, which facilitates the melting. Liquid In2O3 has good electrical conductivity so that eddy currents are induced in the melt close to the crucible wall. This in turn induces a counter magnetic field that ultimately leads to levitation of a portion of the molten In2O3. The amount of the levitated material depends on the mutual RF coil–crucible position, their configurations as well as other components of a growth furnace. A consequence of the partial levitation of In2O3 melt is the formation of a liquid neck between the levitated and the quiescent melt portions. This neck is crucial as it acts as a seed during the crystallization process. The neck can be further shaped by controlled overheating or soaking. By cooling down, two single crystals are formed on the opposite sides of the seed. We named this new crystal growth technique “Levitation-Assisted Self-Seeding Crystal Growth Method”. It is in principle applicable to any oxides whose melts are electrically conductive. Thanks to this method we have successfully grown truly bulk In2O3 single crystals from the melt for the first time worldwide.

Experimental evidence for interaction of water vapor and platinum crucibles at high temperatures : Implications for volatiles from igneous rocks and minerals

The extraction of water from igneous rocks and minerals is classically achieved by induction heating of a platinum alloy crucible where the sample has been deposited. Here, we show that chemical interaction between water and Pt–10%Rh crucibles occurs at high temperature. Known amounts of water were reacted with a Pt crucible held at high temperatures (900–1300°C) for 5–10min and then recovered. The experiments show that on average 20% of the water was lost to the crucible during the reaction, and that the isotopic composition of the remaining water was shifted by up to 25‰. Only 20–50% of the lost water was recoverable by re-heating the crucible at 1300°C. Repeated experiments using the same standard water on the crucible showed a decrease of the isotopic shift to only 2‰. This is compatible with a memory effect of the Pt–10%Rh crucible. We propose that a large amount (at least several tens of μmol) of water remains trapped in the crucible and that partial isotopic exchange between trapped and introduced water affects subsequent isotopic composition of injected water. We conclude that the use of Pt alloys, as crucibles or foils, to extract water from rocks or minerals should be avoided. The interaction highlighted in this study shed light on previously inconsistent observations made on several mantle-derived samples. Fourteen basaltic samples were also re-analyzed without using a metal crucible and show isotopic compositions of hydrogen enriched by 10–20‰ in deuterium relative to previous studies. The isotopic composition of the upper mantle is closer to −60‰, rather than −80‰ as postulated earlier.

Assessment of Quality of Ti Alloys Melted in Induction Furnace with Ceramic Crucible

In this work, the possibility of melting titanium alloys in vacuum induction furnaces in metal and ceramic crucibles and in ceramic crucibles with coatings deposited by the plasma-spray method or by hand using a brush was evaluated. The effect of the crucible material and the coating material on the chemical composition, microstructure and alloy properties was studied. The main criterion for evaluating the suitability of individual crucibles was the content of oxygen in the molten alloys and of impurities remaining as a result of the reaction of the liquid alloy with the crucible and coating material.

Influence of crucible geometry and position on the induction heating process in crystal growth systems

A series of 2D finite element numerical simulations of induction heating process for an oxide Czochralski crystal growth system has been done for different shapes and locations of a metal crucible. Comparison between the computational results shows the importance of crucible shape, geometry and its position with respect to the RF-coil on the electromagnetic field and heat generation distribution in the growth setup.

Numerical study of heat transport and fluid flow during different stages of sapphire Czochralski crystal growth

For different stages of Czochralski crystal growth of sapphire, the flow and temperature field have been studied numerically using the finite element method. The configuration usually used in a real Czochralski crystal growth process consists of a crucible, active afterheater, induction coil with two parts, insulation, crystal, melt and gas. At first the volumetric distribution of heat generation inside the metal crucible and afterheater was calculated. Using this heat distribution as a source the fluid flow and temperature field in the whole system as well as the crystal–melt interface were computed. It was shown that during the last stage of the growth process, the temperature maximum of the system is located at the crucible free surface and the crystal–melt interface has the highest deflection toward the melt.

Influence of the crucible bottom shape on the heat transport and fluid flow during the seeding process of oxide Czochralski crystal growth

AbstractFor the seeding process of oxide Czochralski crystal growth, influence of the crucible bottom shape on the heat generation, temperature and flow field of the system and the seed‐melt interface shape have been studied numerically using the finite element method. The configuration usually used in a real Czochralski crystal growth process consists of a crucible, active afterheater, induction coil with two parts, insulation, melt, gas and seed crystal. At first, the volumetric distribution of heat inside the metal crucible and afterheater inducted by the RF‐coil was calculated. Using this heat generation in the crucible wall as a source the fluid flow and temperature field of the entire system as well as the seed‐melt interface shape were determined. We have considered two cases, flat and rounded crucible bottom shape. It was observed that using a crucible with a rounded bottom has several advantages such as: (i) The position of the heat generation maximum at the crucible side wall moves upwards, compared to the flat bottom shape. (ii) The location of the temperature maximum at the crucible side wall rises and as a result the temperature gradient along the melt surface increases. (iii) The streamlines of the melt flow are parallel to the crucible bottom and have a curved shape which is similar to the rounded bottom shape. These important features lead to increasing thermal convection in the system and influence the velocity field in the melt and gas domain which help preventing some serious growth problems such as spiral growth. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical investigation of heat transport and fluid flow during the seeding process of oxide Czochralski crystal growth Part 1: non‐rotating seed

AbstractFor the seeding process of oxide Czochralski crystal growth, the flow and temperature field of the system as well as the seed‐melt interface shape have been studied numerically using the finite element method. The configuration usually used initially in a real Czochralski crystal growth process consists of a crucible, active afterheater, induction coil with two parts, insulation, melt, gas and non‐rotating seed crystal. At first the volumetric distribution of heat inside the metal crucible and afterheater inducted by the RF coil was calculated. Using this heat source the fluid flow and temperature field were determined in the whole system. We have considered two cases with respect to the seed position: (1) before and (2) after seed touch with the melt. It was observed that in the case of no seed rotation (ωseed = 0), the flow pattern in the bulk melt consists of a single circulation of a slow moving fluid. In the gas domain, there are different types of flow motion related to different positions of the seed crystal. In the case of touched seed, the seed‐melt interface has a deep conic shape towards the melt. It was shown that an active afterheater and its location with respect to the crucible, influences markedly the temperature and flow field of the gas phase in the system and partly in the melt. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical Study of Heat Transport and Fluid Flow of Melt and Gas during the Seeding Process of Sapphire Czochralski Crystal Growth

For the seeding process of the Czochralski crystal growth of sapphire, the flow and temperature field with a nonflat melt−gas interface have been studied numerically using the finite element method. The configuration usually used initially in a real Czochralski crystal growth process consists of a crucible, active afterheater, induction coil with two parts, insulation, melt, and gas. At first, the electromagnetic field produced by the radio frequency (RF) coil in the whole system and the volumetric distribution of heat inside the metal crucible and afterheater were calculated. Using this heat distribution as a source, the fluid flow and temperature field were determined in the whole system. We have considered two cases: (1) configuration without a gap between crucible and afterheater and (2) with a gap, corresponding to an often used growth situation in our lab. It was shown that an active afterheater and its location with respect to the crucible influences markedly the temperature and flow field of the ...

Bridgman-grown zinc oxide single crystals

Zinc oxide single crystals were obtained by solidification of a melt contained in an iridium crucible. To the authors knowledge this is the first report on crystal growth of zinc oxide from the melt using an inductively heated metal crucible. This proves that under particular conditions metals are capable of withstanding liquid zinc oxide at high temperatures. Optical microscopy as well as X-ray rocking curve measurements reveal the high crystalline quality of the wafers with full-width at half-maximum values of 22 arcsec. Annealing of as-grown samples was observed to have a big influence on optical properties.

Numerical study of induction heating and heat transfer in a real Czochralski system

The equations of induction heating and heat transport have been solved for a real Czochralski crystal growth system, using the ENTWIFE package (finite-element method). The configuration usually used in dielectric crystal growth consists of a crucible, afterheater, induction coil with two parts and insulation. At first the electromagnetic field produced by the RF coil in the whole system and the generated heat inside the metal crucible and afterheater was calculated. Using this as a heat source then the temperature field and air convection inside the crucible and afterheater was determined. We have considered two cases: (1) configuration without a gap between crucible and afterheater and (2) with a gap corresponding to an often used growth situation. In both cases it was observed that there are two separate eddies of air convection with approximately equal strength and opposite rotation. Concerning the temperature field, the maximum temperature is in the crucible wall and the minimum is in the bottom corner of the crucible insulation. Along the axis of symmetry, in the first case the temperature is approximately constant and then drops close to the afterheater hole. But in the second case the temperature in the crucible is constant, decreases in the gap and is constant in the afterheater until it drops near its hole. This behavior has been observed during experimental measurements in the lab, too.